Systems and methods for beamforming training in wireless local area networks

ABSTRACT

Presently disclosed are systems and methods for beamforming training in WLANs. In various embodiments, there are unified MIMO beamforming training procedure, which includes a training period in which an initiator transmits multiple unified training frames for performing a transmit-beamforming training of the initiator and a receive-beamforming training of one or more responders; a feedback period in which each responder replies with a beamforming-feedback response; and an acknowledgement period during which the initiator transmits respective acknowledgement frames to the one or more responders from which responses were received. Rules for restricted random access in various slots of the feedback period may be implemented, to address response contention between multiple qualifying responders.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a non-provisional filing of, and claimsbenefit under 35 U.S.C. § 119(c) from, U.S. Provisional PatentApplication Ser. No. 62/306,619, filed Mar. 10, 2016, entitled “SYSTEMSAND METHODS FOR BEAMFORMING TRAINING IN WIRELESS LOCAL AREA NETWORKS,”and U.S. Provisional Patent Application Ser. No. 62/335,518, filed May12, 2016, entitled “SYSTEMS AND METHODS FOR BEAMFORMING TRAINING INWIRELESS LOCAL AREA NETWORKS,” both incorporated herein by reference intheir entirety.

TECHNICAL FIELD

This disclosure relates to systems and methods for beamforming trainingin wireless local area networks (WLANs), such as Institute of Electricaland Electronics Engineers (IEEE) 802.11ay WLANs.

BACKGROUND

Countless devices and networks around the globe operate according to oneor more IEEE 802.11 standards for engaging in wireless communications.These communications typically occur in the 2.4-GHz and 5-GHz bands,though other bands are used as well.

OVERVIEW OF DISCLOSED EMBODIMENTS

Presently disclosed are systems and methods for beamforming training inWLANs.

One embodiment takes the form of a method comprising a responder devicereceiving, from an initiator device, a message frame containingscheduling information that announces a training period and a feedbackperiod for MIMO beamforming training; the responder device receiving,from the initiator device, at least one training frame during theannounced training period; the responder device transmitting abeamforming-feedback response to the initiator device during theannounced feedback period, the beamforming-feedback response identifyinga preferred beam for the responder device; and the responder devicereceiving at least one acknowledgment frame from the initiator device.

One embodiment takes the form of a method comprising a responder devicereceiving, from an initiator device, a message frame containingscheduling information that announces a training period and a feedbackperiod for MIMO beamforming training; the responder device receiving,from the initiator device, at least one training frame during theannounced training period, each of the at least one training framehaving a plurality of training sequences appended to an end of saidtraining frame, wherein the number of training sequences isrepresentative of a number of receive beams of the responder to betrained; the responder device, for each of the at least one trainingframes, sequentially receiving on each of a plurality of receive beamsduring the appended training sequences; the responder device determininga best receive beam of its plurality of receive beams trained in thetraining period; the responder device transmitting abeamforming-feedback response to the initiator device during one of aplurality of feedback period time slots associated with the receivebeams of the initiator device in the announced feedback period, thebeamforming-feedback response transmitted on a transmit beam associatedwith the best receive beam of the responder device and respectivetransmit beam of the initiator device; and the responder devicereceiving at least one acknowledgment frame from the initiator device.

One embodiment takes the form of a method comprising an initiator devicetransmitting, to a plurality of responder devices, a message framecontaining scheduling information that announces a training period and afeedback period for MIMO beamforming training; the initiator devicetransmitting, to the plurality of responder devices, a plurality oftraining frames, each frame sequentially transmitted using a respectivebeam, during the announced training period, and each of the trainingframes having a plurality of training sequences appended to an end ofsaid training frame, wherein the number of training sequences isrepresentative of a number of receive beams of the initiator to betrained; the initiator device sequentially receivingbeamforming-feedback responses on the receive beams of the initiator tobe trained, said responses received from at least a subset of theplurality of responder devices during the announced feedback period; andthe initiator device transmitting, responsive to the receivedbeamforming-feedback responses, one or more acknowledgement frames tothe subset of the plurality of responder devices.

One embodiment takes the form of a method comprising an initiator devicetransmitting, to a plurality of responder devices, a message framecontaining scheduling information that announces a training period and afeedback period for MIMO beamforming training; the initiator devicetransmitting, to the plurality of responder devices, a plurality oftraining frames, each frame transmitted using a respective beam, duringthe announced training period; the initiator device receivingbeamforming-feedback responses from at least a subset of the pluralityof responder devices during the announced feedback period; and theinitiator device transmitting, responsive to the receivedbeamforming-feedback responses, one or more acknowledgement frames tothe subset of the plurality of responder devices.

Another embodiment takes the form of an initiator device comprising awireless-communication interface; a processor; and data storagecontaining instructions executable by the processor for causing theinitiator device to carry out at least the functions listed in thepreceding paragraph.

Another embodiment takes the form of a unified MIMO beamforming trainingprocedure, which includes a training period in which an initiatortransmits multiple unified training frames for performing atransmit-beamforming training of the initiator and a receive-beamformingtraining of one or more responders; a training-feedback period in whicheach responder replies with a training-feedback frames; and anacknowledgement period during which the initiator transmits respectiveacknowledgement frames to the one or more responders.

Moreover, any of the variations and permutations described in thisdisclosure can be implemented with respect to any embodiments, includingwith respect to any method embodiments and with respect to any systemembodiments. Furthermore, this flexibility and cross-applicability ofembodiments is present in spite of the use of slightly differentlanguage (e.g., process, method, steps, functions, set of functions, andthe like) to describe and or characterize such embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example sector level sweep (SLS) training procedure,in accordance with at least one embodiment.

FIG. 2 depicts an example sector sweep (SSW) frame format, in accordancewith at least one embodiment.

FIG. 3 depicts an example SSW-field format, in accordance with at leastone embodiment.

FIG. 4A depicts a first example SSW-feedback-field format, in accordancewith at least one embodiment.

FIG. 4B depicts a second example SSW-feedback-field format, inaccordance with at least one embodiment.

FIG. 5 depicts a first example packet structure, in accordance with atleast one embodiment.

FIG. 6 depicts a first example timing diagram, in accordance with atleast one embodiment.

FIG. 7 depicts a second example timing diagram, in accordance with atleast one embodiment.

FIG. 8 depicts a second example packet structure, in accordance with atleast one embodiment.

FIG. 9 depicts a third example timing diagram, in accordance with atleast one embodiment.

FIG. 10 depicts a fourth example timing diagram, in accordance with atleast one embodiment.

FIG. 11 depicts an example wireless-communication scenario, inaccordance with at least one embodiment.

FIG. 12 depicts an example wireless-communication device, in accordancewith at least one embodiment.

Moreover, before proceeding with this disclosure, it is noted that theentities, connections, arrangements, and the like that are depictedin—and described in connection with—the various figures are presented byway of example and not by way of limitation. As such, any and allstatements or other indications as to what a particular figure“depicts,” what a particular element or entity in a particular figure“is” or “has,” and any and all similar statements—that may in isolationand out of context be read as absolute and therefore limiting—can onlyproperly be read as being constructively preceded by a clause such as“In at least one embodiment . . . ” And it is for reasons akin tobrevity and clarity of presentation that this implied leading clause isnot repeated ad nauseum in the below detailed description of thedrawings.

DETAILED DESCRIPTION

Overview of WLAN. A WLAN in Infrastructure Basic Service Set (BSS) modehas an Access Point/Personal BSS (PBSS) Control Point (AP/PCP) for theBSS and one or more stations (STAs) (e.g., client devices) associatedwith the AP/PCP. The AP/PCP typically has access or interface to aDistribution System (DS) or another type of wired/wireless network thatcarries traffic in and out of the BSS. Traffic to STAs that originatesfrom outside the BSS arrives through the AP/PCP and is delivered to theSTAs. Traffic originating from STAs to destinations outside the BSS issent to the AP/PCP to be delivered to the respective destinations.Traffic between STAs within the BSS may also be sent through the AP/PCPwhere the source STA sends traffic to the AP/PCP and the AP/PCP deliversthe traffic to the destination STA. Such traffic between STAs within aBSS is really peer-to-peer traffic. Such peer-to-peer traffic may alsobe sent directly between the source and destination STAs with a directlink setup (DLS) using an 802.11e DLS or an 802.11z tunneled DLS (TDLS).A WLAN using an Independent BSS (IBSS) mode has no AP, and compatibledevices simply communicate directly with each other. This mode ofcommunication is referred to as an “ad-hoc” mode of communication.

Using the 802.11ac infrastructure mode of operation, the AP/PCP maytransmit a beacon on a fixed channel, usually the primary channel. Thischannel may be 20 megahertz (MHz) wide, and is the operating channel ofthe BSS. This channel is also used by the STAs to establish a connectionwith the AP/PCP. The fundamental channel-access mechanism in an 802.11system is Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA). In this mode of operation, every STA, including the AP/PCP,will sense the primary channel. If the channel is detected to be busy,the STA backs off. Hence only one STA may transmit at any given time ina given BSS.

In 802.11n (as discussed in IEEE Std 802.11™-2012: Wireless LAN MediumAccess Control (MAC) and Physical Layer (PHY) Specifications), HighThroughput (HT) STAs may also use a 40-MHz-wide channel forcommunication. This is achieved by combining the primary 20-MHz-widechannel with an adjacent 20-MHz-wide channel to form a 40-MHz-widecontiguous channel.

In 802.11ac (as discussed in IEEE Std 802.11ad™-2012: Part 11: WirelessLAN Medium Access Control (MAC) and Physical Layer (PHY) SpecificationsAmendment 3: Enhancements for Very High Throughput in the 60 GHz Band),Very High Throughput (VHT) STAs may support 20-MHz-wide, 40-MHz-wide,80-MHz-wide, and 160-MHz-wide channels. The 40-MHz-wide channels and the80-MHz-wide channels are formed by combining contiguous 20-MHz-widechannels in a manner that is similar to what is described above inconnection with 802.11n. A 160-MHz-wide channel may be formed either bycombining 8 contiguous 20-MHz-wide channels, or by combining 2non-contiguous 80-MHz-wide channels in what is also referred to at timesas an “80+80 configuration.” For the 80+80 configuration, the data,after channel encoding, is passed through a segment parser that dividesit into two streams. Inverse Fast Fourier Transform (IFFT) processingand time-domain processing are performed on each stream separately. Thestreams are then mapped on to the two channels, and the data istransmitted. At the receiver, this mechanism is reversed, and thecombined data is delivered to the MAC of the receiver.

Sub-1-gigahertz (GHz) modes of operation are supported by 802.11af (asdiscussed in IEEE P802.11ac™/D1.0: Part 11, Wireless LAN Medium AccessControl (MAC) and Physical Layer (PHY) specifications. Amendment 5:Enhancements for Very High Throughput for Operation in Bands below 6GHz) and 802.11ah (as discussed in IEEE 802.11-10/0258r0, MAC and PHYProposal for 802.11af, March 2010.). (see also IEEE 802.11-10/0001r13,Sub 1 GHz license-exempt PAR and 5C, July 2010.) For thesespecifications, the channel operating bandwidths, as well as thecarriers, are reduced relative to those used in 802.11n and 802.11ac.802.11af supports 5-MHz, 10-MHz, and 20-MHz bandwidths in the TV WhiteSpace (TVWS) spectrum, and 802.11ah supports 1-MHz, 2-MHz, 4-MHz, 8-MHz,and 16-MHz bandwidths using non-TVWS spectrum. A possible use case for802.11ah is support for Meter Type Control (MTC) devices in a macrocoverage area. MTC devices may have limited capabilities including onlysupport for only limited bandwidths, but also include a requirement fora very long battery life.

WLAN systems—such as 802.11n, 802.11ac, 802.11af, and 802.11ah—thatsupport multiple channels and multiple channel widths include a channelthat is designated as the primary channel. The primary channel may, butdoes not necessarily, have a bandwidth equal to the largest commonoperating bandwidth supported by all STAs in the BSS. The bandwidth ofthe primary channel is therefore limited by the STA (among the STAs thatare operating in a BSS) that supports the smallest bandwidth operatingmode (as the maximum supported channel-bandwidth operating mode for theparticular STA). In the example of 802.11ah, the primary channel may be1 MHz wide if there are STAs (e.g. MTC-type devices) that only support a1-MHz mode even if the AP/PCP and other STAs in the BSS support, e.g., a2-MHz, a 4-MHz, an 8-MHz, a 16-MHz, and/or one or more otherchannel-bandwidth operating modes in excess of the 1-MHzchannel-bandwidth operating mode. All carrier sensing, as well as NAVsettings, depend on the status of the primary channel; i.e., if theprimary channel is busy, for example, due to a STA that supports only a1-MHz operating mode currently transmitting to the AP, then the entireavailable frequency bands are considered busy even though majority of itstays idle and available.

In the United States, the available frequency bands that can be used for802.11ah are from 902 MHz to 928 MHz. In Korea, it is from 917.5 MHz to923.5 MHz; and in Japan, it is from 916.5 MHz to 927.5 MHz. The totalbandwidth available for 802.11ah is between 6 and 26 MHz depending onthe country code.

To improve spectral efficiency, 802.11ac has introduced the concept ofdownlink (DL) multi-user (MU) multiple-in-multiple-out (MIMO) (MU-MIMO)transmission to multiple STAs in the same symbol's time frame, e.g.during a downlink OFDM symbol. The potential for the use of downlinkMU-MIMO is also currently considered for 802.11ah. One may note thatsince downlink MU-MIMO, as it is used in 802.11ac, uses the same symboltiming to multiple STAs, interference of the waveform transmissions tomultiple STAs is not an issue. However, all STAs involved in MU-MIMOtransmission with the AP/PCP must use the same channel or band, whichlimits the operating bandwidth to the smallest channel bandwidth that issupported by the STAs that are included in the MU-MIMO transmission withthe AP/PCP.

802.11ad. 802.11ad is an amendment to the WLAN standard, which specifiesthe MAC and PHY layers for very high throughput (VHT) in the 60 GHzband.

802.11ad has the following features:

-   -   1. 802.11ad supports data rates up to 7 gigabits (Gbits) per        second (s) (Gbits/s).    -   2. 802.11ad supports three different modulation modes:        -   a. Control PHY with single carrier and spread spectrum;        -   b. Single Carrier PHY; and        -   c. OFDM PHY.    -   3. 802.11ad uses the 60-gigahertz (GHz) unlicensed band, which        is available globally. At 60 GHz, the wavelength is 5        millimeters (mm), which makes compact antennas and antenna        arrays possible. Such an antenna can create narrow        radio-frequency (RF) beams at both the transmitter and the        receiver, which effectively increases the coverage range and        reduces interference.    -   4. 802.11ad has a frame structure that facilitates a mechanism        for beamforming training (discovery and tracking). The        beamforming training protocol includes two components: a sector        level sweep (SLS) procedure and a beam refinement protocol (BRP)        procedure. The SLS procedure is used for transmit beamforming        training; the BRP procedure enables receive beamforming training        as well as iterative refinement of both the transmit and receive        beams.

MIMO transmissions, including both single-user-(SU)-MIMO and MU-MIMO,are not supported by 802.11ad.

Sector Level Sweep (SLS). An example SLS training procedure is shown inFIG. 1.

SLS training may be performed using Beacon frame or SSW frame. WhenBeacon frame is utilized, the AP/PCP repeats the Beacon frame withmultiple beams/sectors within each Beacon interval (BI) and multipleSTAs can perform BF training simultaneously. However, due to the size ofBeacon frame, it is no guarantee that the AP/PCP can sweep all thesectors/beams within one BI. Thus a STA may need to wait multiple BIs tocomplete ISS training, and latency may be an issue. A SSW frame may beutilized for point to point BF training. A SSW frame may be transmittedusing control PHY and the frame format is shown in FIG. 2.

An example SSW-field structure is shown in FIG. 3.

A first example SSW-feedback field is shown in FIG. 4A. This correspondsto when this is transmitted as part of an ISS.

A second example SSW-feedback field is shown in FIG. 4B. Thiscorresponds to when this is not transmitted as part of an ISS.

Beamforming Refinement Protocol (BRP). Beam refinement is a processwhere a STA can improve its antenna configuration (or antenna weightvectors) both for transmission and reception. In the beam refinementprocedure, BRP packets are used to train the receiver and transmitterantenna. There are two types of BRP packets: BRP-RX packets and BRP-TXpackets. BRP packet may be carried by a DMG PPDU followed by a training(TRN) field containing an AGC field and a transmitter or receivertraining field as shown in FIG. 5.

A value of N in FIG. 5 is the Training Length given in the header filed,which indicates that the AGC has 4N subfields and that the TRN-R/T fieldhas 5N subfields. The CE subfield is the same as the one in the preambledescribed in the previous section. All subfields in the beam trainingfield are transmitted using rotated π/2-BPSK modulation.

BRP MAC frame is an Action No ACK frame, which has the following fields:

-   -   Category    -   Unprotected DMG Action    -   Dialog Token    -   BRP Request field    -   DMG Beam Refinement element    -   Channel Measurement Feedback element 1    -   . . .    -   Channel Measurement Feedback element k

802.11ay (TGay). Requirements of 802.11ay. Task Group ay (TGay),approved by IEEE in March 2015, is expected to develop an amendment thatdefines standardized modifications to both the IEEE 802.11 physicallayers (PHY) and the IEEE 802, 11 medium access control layer (MAC) thatenables at least one mode of operation capable of supporting a maximumthroughput of at least 20 gigabits per second (measured at the MAC dataservice access point), while maintaining or improving the powerefficiency per station. This amendment also defines operations forlicense-exempt bands above 45 GHz while ensuring backward compatibilityand coexistence with legacy directional multi-gigabit stations (definedby IEEE 802.11ad-2012 amendment) operating in the same band.

Although much higher maximum throughput than that of 802.11ad is theprimary goal of TGay, some members of the group also discussed includingmobility and outdoor support. More than ten different use cases areconsidered and analyzed in terms of throughput, latency, operationenvironment and applications (as discussed in IEEE 802.11-2015/0625r2,“IEEE 802.11 TGay Use Cases”, Huawei, et. al.).

Since 802.11ay will operate in the same band as legacy standards, it isrequired that the new technology will ensure backward compatibility andcoexistence with legacies in the same band.

Beamforming in 802.11. BF Training Efficiency. BF training proceduresspecified in 802.11ad may achieve good performance if both initiator andresponder train their transmitter/receiver beams respectively, whichrequires four training periods, and each training period may involvetraining and measurement on multiple beams. With channel/antennareciprocity assumption, beams/sectors trained from downlink may be usedfor uplink too. Existing BF training procedures need to train initiatorTX/RX and responder TX/RX to achieve good BF gain, which is notefficient.

Existing BF training procedures utilizing Beacon frames allow multipleSTAs to perform measurements and select their best transmit beam fromthe AP/PCP. However, it may take several BIs until the STAs may completethe training. Latency is also an issue. Beyond this, there is no BFtraining procedure which may allow multiple STAs to trainsimultaneously.

Efficient BF training procedures are needed to support: ISS TXSS and ISSRXSS training using a unified training frame; and a low latencymechanism to train multiple users simultaneously. Disclosed herein aremethods, procedures, and systems for providing and/or supporting suchefficient MIMO BF training. In some embodiments, there are disclosedunified multicast training procedures.

Embodiment 1

In at least one embodiment, a unified multicast training procedure isused by an AP/PCP to train:

-   -   All the STAs which intend to perform initial and/or updated MIMO        BF training/tracking. Note, the STAs may or may not be        associated with the AP/PCP. In other words, unassociated STAs        may perform MIMO BF training with the AP/PCP.    -   All the associated STAs which intend to perform initial and/or        updated MIMO BF training/tracking.    -   A group of STAs identified by the AP/PCP. The AP/PCP may group        STAs for MIMO BF training/tracking using different criteria.

In an embodiment, a unified multicast training procedure may beperformed using: BTI, A-BFT frame exchanges; In schedule based ServicePeriod (SP); In Contention Based Access Period (CBAP).

Various disclosed embodiments can be used in channel-bonding scenarios.

Note, herein xIFS is used to indicate the inter-frame spacing in theTraining/FB TXOP. Alternatively, more than one inter-frame spacing maybe utilized in this procedure. For example, xIFS1 may be used betweentwo Training Frames. xIFS2 may be used between the Training period andFB period. xIFS3 may be used between frames transmitted in the FBperiod. xIFS4 may be used between the FB period and MU ACK/M-STA ACK.

Note a sector/beam/AVW mentioned in this embodiment may be formed usingsingle Phased Antenna Array (PAA) or multiple PAAs, or other type ofantennas. When the transmitter/receiver sweep sectors/beams/AVWs, it mayswitch within one PAA or go through all the sectors/beams/AVWs usingmultiple/all PAAs.

In an embodiment, a unified multicast/broadcast MIMO BF trainingprocedure includes: a training period, a training feedback period, andan acknowledgment period. In the training period, an initiator maytransmit multiple unified training frames which may be used to performtransmit BF training of the initiator and the receive BF training of theresponder(s). in the training feedback period, one or more respondersmay reply the training feedback frames. The training feedback frames maybe transmitted using a random access, scheduled access or poll basedaccess. In the acknowledgement period, the initiator may transmitacknowledgement frame to the responder(s).

An exemplary procedure is given in FIG. 6, which depicts a first exampletiming diagram, in accordance with at least one embodiment. The timingdiagram of FIG. 6 comprises an example unified multicast/broadcasttraining procedure as generally set forth below.

Detailed procedures for AP/PCP and non-AP/non-PCP STAs are given below.

Note, TXOP periods allocated using this mechanism do not persist beyonda beacon interval.

Initiator (e.g., AP/PCP) procedure. In one embodiment, an initiator mayinclude scheduling information in a Beacon frame, which may announce aService Period for MIMO BF training/feedback. The initiator may definethe starting time (which may be a time offset relative to the Beaconframe) and duration for the MIMO BF training/feedback period.Alternatively, the initiator may acquire media through contention. In athird option, the initiator may utilize a modified Beacon frame as thetraining frame.

The initiator may transmit N Training Frames in the training period. Thevalue of N may be indicated in each Training Frame. Alternatively, theremaining number of Training Frames may be signaled in each TrainingFrame. Each time, a Training Frame may be transmitted using asector/beam/antenna vector weight (AVW). Different Training Frames maybe transmitted using different sectors/beams/AVWs. The Training Framesmay be separated by an xIFS period. Alternatively, each time, one ormore Training Frames may be transmitted using one or moresectors/beams/AVWs.

The PLCP header of the Training Frame may indicate: BSSID/Color whichmay be used to identify the initiator and/or the corresponding BSS;and/or K extra AGC/training sequences (i.e., TRN field) may be appendedat the end of the Training Frame. K may depend on the maximum number ofreceive sectors/beams/AVWs to be trained.

The MAC body of the Training Frames may carry duration, sector/beam/AVWID, the feedback request/preference information, the ACK info, etc.

Transmission of the Training Frame: Each time, the initiator maytransmit one Training Frame using a sector/beam/AVW. Alternatively, theinitiator may transmit Training Frame(s) using multiplesectors/beams/AVWs concurrently. The initiator may transmit the extra Ktraining sequences using the same sector/beam/AVW as used by the othersection of the Training Frame. Depending on the purpose of the MIMO BFtraining, the Training Frame may be coded and modulated using the lowestMCS level. Alternatively, if the purpose of the Training/FB TXOP is forBF tracking/refinement/updates, other MCS levels may be utilized.

In an xIFS period after the end of the Training period, the initiatormay prepare to receive feedbacks from responders, which may be referredas the Feedback period. The FB period may be used to carry multiplefeedback frames using multiple time slots. The length of each feedbacktime slot, which may be signaled in the Beacon Frame and/or previouslytransmitted Training Frame, may or may not be the same. In the case thatthe FB time slot has a fixed length/duration, the initiator may expectthe responder to truncate the FB transmission at the boundary if needed.The FB period may be a multiple access period, and the possible FB typemay be: FB period without polling; or FB period with polling.

For the type FB period without polling, the type may be random access orscheduled based access. In random access, multiple responders contendfor multiple time slots to transmit. The initiator may announcerestricted random access on some time slots in the Beacon frame or theTraining frame before the FB period. In that case, only the responderswhich may satisfy the restriction may respond in that time slot. Inscheduled based access, the initiator may schedule the transmissions inTraining Frame(s) or Beacon Frame(s) or other types ofcontrol/management frames transmitted before the Training/FB TXOP.

For the type FB period with polling, each FB time slot may start with apolling frame transmitted from the initiator. In the xIFS period afterthe polling frame, the responders may transmit FB frame(s). The pollingframe may carry indication of a responder or a group or a sub-group ofresponders who may transmit using this FB time slot. FB periods withpolling may be random access or scheduled based access. In randomaccess, multiple responders which may qualify for the transmission maycontend for the FB time slot using a given random access protocol. Inscheduled based access, the initiator may poll one responder for the FB.The polled responder may transmit FB frame xIFS period after the pollingframe. In one embodiment, the polling frame may be omitted for the firstFB frame if the last Training Frame may be interpreted as a firstpolling frame. In some embodiments, the polling frame may be transmittedusing the quasi-Omni weight or other weight. The polling frame may betransmitted using a low data rate coding and modulation scheme, e.g.,the lowest MCS.

In one embodiment, the FB period may be used to carry acknowledgementfrom the initiator. xIFS time after the reception of a FB frame, theinitiator may transmit an acknowledgement frame to the responder if thepreviously transmitted FB frame may be successfully decoded.

xIFS period after the end of the FB period, the initiator may prepare totransmit one or more acknowledgement frames. In one embodiment, theinitiator may transmit a multi-STA acknowledgement (M-STA ACK) frame tomultiple responders. The M-STA ACK may be transmitted using quasi-Omniweight and modulated and coded using the lowest MCS level. The M-STA ACKframe may be repeated in the time and/or frequency domain to improve thereliability. In another embodiment, the initiator may transmit multipleACK/BA frames to multiple responders. The transmission may be separatedby time period xIFS. Each ACK/BA frame may be transmitted using the bestsector/beam/AVW selected based on the feedbacks transmitted in FBperiod. Alternatively, the initiator may transmit an ACK announcementframe xIFS time after the end of FB frame. The announcement frame may beused to broadcast ACK/BA scheduling information using the lowest MCS andquasi-Omni antenna patterns. xIFS time after the announcement frame, theinitiator may start transmitting the first ACK/BA frame. More ACK/BAframe may follow.

Responder (e.g., non-AP/non-PCP STAs) procedure. In some embodiments, aresponder may participate in the Training/FB period if one or moreconditions met:

-   -   The responder may not have NAV set during the TXOP.    -   The responder may intend to perform MIMO/BF training with the        initiator.    -   The responder may be polled by the initiator.    -   The responder may qualify the certain condition(s) carried in        Beacon and/or Training Frame to perform MIMO/BF training using        the scheduled Training/FB period.    -   The responder may monitor the Beacon frame which may announce        the schedule of the Training/FB TXOP.    -   The responder may successfully detect one of the Training        Frames, and notice the Training/FB TXOP.

The responder may successfully detect one of the Training Frames using aquasi-Omni beam or other sector/beam/AVW selected. Based on theinformation carried in the MAC frame of the Training Frame, theresponder may know the total number of Training Frames transmitted inthe training period and/or the remaining number of Training Frames to betransmitted. Alternatively, the total number of Training Framestransmitted in the training period may be carried in a Beacon frame.Based on the information carried in the Training Frame PLCP header, theresponder may be notified that K extra AGC/Training sequences may beappended to the end of the current Training Frame to allow responderreceive beam training. If K is greater than or equal to the number ofreceiving sectors/beams/AVWs to be trained, the responder may switch itsreceiving sectors/beams/AVWs over all the possible combinations. In thecase K is greater than the number of receiving sectors/beams/AVWs to betrained, the responder may use the extra AGC/Training sequence(s) onselected receiving sectors/beams/AVWs to get more accurate measurements.If K is less than the number of receiving sectors/beams/AVWs to betrained, the responder may check its training history, if any, andselect K receiving sectors/beams/AVWs. Alternatively, the responder maykeep a record of trained beams and complete the receiving MIMO BFtraining using multiple Training/FB TXOPs.

The responder may begin feedback period xIFS time after the end of thetraining period. The responder may estimate the length of the trainingperiod and prepare FB if needed in the following FB period based on thetype of FB period. Alternatively, the responder may know the duration ofthe Training Period through the Beacon Frame which schedule the TrainingTXOP and thus know the boundary of the training period and FB period.For FB periods without polling:

-   -   With random access FB, the responder may determine a time slot        to transmit the FB using certain random access protocol. The        responder may start the FB transmission at the beginning of the        time slot.    -   With schedule based FB, the responder may transmit at the        beginning of the scheduled time slot.

For FB periods with polling:

-   -   With random access FB, the responder may determine a time slot        to transmit the FB using certain random access protocol. xIFS        time after the polling frame, the responder may transmit the FB        frame. Alternatively, the responder may be triggered by the        polling frame to start the random access protocol for the FB        transmission.    -   With schedule based FB, the initiator may poll one responder for        the FB. The polled responder may transmit FB frame xIFS period        after the polling frame.

BF transmission of the FB frame. If antenna/channel reciprocity isassumed, the FB frame may be transmitted using the best sector/beam/AVWtrained as in the Training period at the responder side. In this case,the best transmit sector/beam/AVW may be the same as the best receivesector/beam/AVW trained at the responder side. Otherwise the respondermay utilize a selected sector/beam/AVW or Quasi-Omni weight.

Coding and modulation of the FB frame. The FB frame may be coded andmodulated using the lowest MCS level. Alternatively, the initiator mayassign MCS level for FB in Training frame or Beacon frame. In a thirdmethod, depending on the beamforming scheme used for FB frame, theresponder may determine the MCS used. For example, if the FB frame istransmitted using a trained narrow beam, the responder may utilizehigher MCS level (MCS with higher data rate). If the FB frame istransmitted using a wide beam or Quasi-Omni beam, the responder mayutilize a lower MCS level.

In one embodiment, the FB period may be used to carry acknowledgementfrom the initiator. xIFS time after the end of a FB frame, the respondermay expect to receive an acknowledgement frame from the initiator. Theresponder may use the trained best receive sector/beam/AVW for thereception. If the responder may not receive anything after yIFS timeperiod, the responder may consider the failure of FB transmission. yIFSmay be longer than xIFS. In the case that each FB time slot may be witha fixed duration, the responder may truncate the transmission at theboundary. The extra FB frame may be needed to complete the feedbackprocedure.

The responder(s) may expect to receive an acknowledgement frame from theinitiator xIFS period after the end of FB period. In one embodiment, theresponder may receive an M-STA ACK frame which may be abroadcast/multicast frame transmitted from the initiator. Each respondermay check the per user field in the frame, which may contain a STA ID.If one STA ID may match the responder's ID, the responder may check theACK/BA field corresponding to the STA ID. In another embodiment, theresponder may receive one or multiple ACK/BA frames from the initiator.One of the ACK/BA frame may be addressed to the responder. The respondermay check the ACK/BA information contained in that frame. Alternatively,the responder may receive an announcement frame xIFS time after the endof FB frame. The announcement frame may contain ACK/BA schedulinginformation to multiple responders. The responder may determine thetime/frequency offset of the expected ACK/BA frame corresponding to theannouncement frame. The responder to check its ACK/BA frame based on thetime/frequency offset. In the case that the responder may not receiveany ACK or receive a negative ACK in the acknowledgement period, theresponder may determine failure of the FB transmission. The respondermay wait for another opportunity to perform training and/or feedback inthe future.

Embodiment 2

With reference to a second embodiment, another unifiedmulticast/broadcast MIMO BF training procedure is disclosed. With thisprocedure, the training/FB TXOP may be composed of three maincomponents—a Training period, a FB period, and an ACK period—which arescheduled and announced by a Training Announcement frame transmitted atthe beginning of the TXOP (as shown in FIG. 7). In one embodiment, thethree components may be transmitted within one TXOP (as shown in FIG.7). In another embodiment, the three components may be transmittedthrough different TXOPs, which may be schedule based and/or contentionbased. The Training announcement frame may or may not present at thebeginning of each TXOP.

Note, TXOP periods allocated using this mechanism do not persist beyonda beacon interval.

FIG. 7 depicts a second example timing diagram, which illustrates asecond example unified multicast/broadcast training procedure with aTraining Announcement frame.

Initiator (e.g., AP/PCP) procedure. An initiator may acquire the mediathrough contention and/or scheduling. In the case of scheduling, aBeacon frame or a frame transmitted in announcement transmissioninterval (ATI) may be used to include the starting time and duration ofthe training/FB TXOP. Alternatively, the initiator may utilize amodified Beacon frame as training frame.

The initiator may transmit a Training Announcement frame to indicate:

-   -   The length of the entire TXOP.    -   Time/Frequency Allocation for training period. For example, the        allocation start time, allocation duration, and allocated        channel index may be defined for the training period. Here the        allocated channel index may be replaced with other type of        signaling, which may be used to uniquely indicate the starting        frequency (or center frequency) and allocated bandwidth.    -   Time/Frequency Allocation for FB period. For example, the        allocation start time, allocation duration, and allocated        channel index may be defined for the FB.    -   Time/Frequency Allocation for acknowledgement period. For        example, the allocation start time, allocation duration, and        allocated channel index may be defined for the acknowledgement        period.

The initiator may transmit N Training Frames in the training period. Nmay be indicated in the Training Announcement frame and/or each TrainingFrame. Alternatively, the remaining number of Training frame may besignaled in each Training Frame. Each time, a Training Frame may betransmitted using a sector/beam/antenna vector weight (AVW). DifferentTraining Frames may be transmitted using different sectors/beams/AVWs.The Training Frames may be separated by an xIFS period. Alternatively,each time, one or more Training Frames may be transmitted using one ormore sectors/beams/AVWs.

The PLCP header of the Training Frame and/or the Training Announcementframe may indicate:

-   -   BSSID/Color which may be used to identify the initiator and/or        the corresponding BSS.    -   K extra AGC/training sequences may be appended at the end of the        Training Frame. K may depend on the maximum number of receive        sectors/beams/AVWs to be trained.

The MAC body of the Training Frames may carry duration, sector/beam/AVWID, the feedback request/preference information, the ACK info etc.Alternatively, the MAC body may not present. Instead, the TrainingAnnouncement frame may carry information about FB request/preferenceinformation, and ACK information etc. One field in PLCP header may beused to indicate the Training Frame may not contain any MAC body. Withthat indication, the SIG field may be overwritten to carry informationsuch as sector/beam/AVW ID. This kind of Training Frame may be referredas a NDP Training Frame. Transmission of the Training Frame may be thesame as discussed previously.

xIFS period after the end of the Training period, the initiator mayprepare to receive feedbacks from responders, which may be referred asFeedback period.

The FB period may be used to carry multiple feedback frames usingmultiple time slots. The length of each feedback time slot, which may besignaled in the Announcement Frame, may or may not be the same. In thecase that the FB time slot is with the fixed length/duration, theinitiator may expect the responder to truncate the FB transmission atthe boundary if needed. The FB period may be a multiple access period,and the possible FB type, which may be signaled in the TrainingAnnouncement Frame, may be FB period without polling or FB period withpolling.

An FB period without polling may be random access or schedule basedaccess. In random access, multiple responders contend multiple timeslots to transmit. The initiator may announce restricted random accesson some time slots in the Training Announcement Frame. In that case,only the responders which may satisfy the restriction may respond inthat time slot. In schedule based access, the initiator may schedule theFB transmissions in Training Announcement Frame or Beacon Frame orTraining Frame or other type of control/management frames transmittedbefore the Training/FB TXOP.

For FB periods with polling, each FB time slot may start with a pollingframe transmitted from the initiator. xIFS period after the pollingframe, the responders may transmit FB frame(s). The polling frame maycarry indication of a responder or a group or a sub-group of responderswho may transmit using this FB time slot. FB periods with polling may berandom access or schedule based. In random access, multiple responderswhich may qualify the transmission may contend for the FB time slotusing certain random access protocol. In schedule based access, theinitiator may poll one responder for the FB. The polled responder maytransmit FB frame xIFS period after the polling frame. In anotherembodiment, the polling frame may be omitted for the first FB frame ifthe last Training Frame may be interpreted as a first polling frame. Insome embodiments, the polling frame may be transmitted using thequasi-Omni weight or other weight. The polling frame may be transmittedusing a low data rate coding and modulation scheme, e.g., the lowestMCS.

In another embodiment, the FB period may be used to carryacknowledgement from the initiator. xIFS time after the reception of aFB frame, the initiator may transmit an acknowledgement frame to theresponder if the previously transmitted FB frame may be successfullydecoded. This kind of transmission may be signaled in the TrainingAnnouncement Frame.

xIFS period after the end of the FB period, the initiator may prepare totransmit one or more acknowledgement frames. In one embodiment, theinitiator may transmit a multi-STA acknowledgement (M-STA ACK) frame tomultiple responders. The M-STA ACK may be transmitted using quasi-Omniweight and modulated and coded using the lowest MCS level. The M-STA ACKframe may be repeated in time and/or frequency domain to improve thereliability. In another embodiment, the initiator may transmit multipleACK/BA frames to multiple responders. The transmission may be separatedby xIFS time period. Each ACK/BA frame may be transmitted using the bestsector/beam/AVW selected based on the feedbacks transmitted in FBperiod. Alternatively, the initiator may transmit an ACK announcementframe xIFS time after the end of FB frame. The announcement frame may beused to broadcast ACK/BA scheduling information using the lowest MCS andquasi-Omni antenna patterns. xIFS time after the announcement frame, theinitiator may start transmitting the first ACK/BA frame. More ACK/BAframe may follow.

Responder (e.g., non-AP/non-PCP STAs) procedure. A responder mayparticipate the Training/FB period if one or more conditions met:

-   -   The responder may not have NAV set during the TXOP.    -   The responder may intend to perform MIMO/BF training with the        initiator.    -   The responder may be polled by the initiator.    -   The responder may qualify the certain condition(s) carried in        Training Announcement Frame, Beacon and/or Training Frame to        perform MIMO/BF training using the scheduled Training/FB period.    -   The responder may monitor the Beacon frame which may announce        the schedule of the Training/FB TXOP.    -   The responder may successfully detect one of the Training        Frames, and notice the Training/FB TXOP.

The responder may detect the Training Announcement Frame, and noticesthe allocation of Training period, FB period, and Acknowledgementperiod. The responder may know the total number of Training Framestransmitted in the training period.

The responder may successfully detect one of the Training Frames using aquasi-Omni beam or other sector/beam/AVW selected. Based on theinformation carried in the MAC frame of the Training Frame, theresponder may know the remaining number of Training Frames to betransmitted. Alternatively, if NDP Training frame is utilized, theresponder may notice that by checking the NDP indication bit in PLCPheader and re-interpret the PLCP header of the Training frame to obtainthe information. Based on the information carried in Training Frame PLCPheader and/or the Training Announcement frame, the responder may noticeK extra AGC/Training sequences may be appended to the end of the currentTraining Frame which may allow the responders to train receive beams. IfK is greater than or equal to the number of receiving sectors/beams/AVWsto be trained, the responder may switch its receiving sectors/beams/AVWsover all the possible combinations. In the case where K is greater thanthe number of receiving sectors/beams/AVWs to be trained the respondermay use the extra AGC/Training sequence on selected receivingsectors/beams/AVWs to get more accurate measurements. If K is less thanthe number of receiving sectors/beams/AVWs to be trained, the respondermay check its training history if any, and select K receivingsectors/beams/AVWs. Alternatively, the responder may keep a record oftrained beams and complete the receiving MIMO BF training using multipleTraining/FB TXOPs.

The responder may begin feedback period xIFS time after the end of thetraining period. The responder may estimate the length of the trainingperiod and prepare FB if needed in the following FB period based on thetype of FB period. Alternatively, the responder may know the duration ofthe Training Period through the Training Announcement Frame and thusknow the boundary of the training period and FB period. FB periods maybe with or without polling.

For FB periods without polling, there may be random access or schedulebased FB. In random access FB, the responder may determine a time slotto transmit the FB using certain random access protocol. The respondermay start the FB transmission at the beginning of the time slot. Inschedule based FB, the responder may transmit at the beginning of thescheduled time slot. The FB scheduling information may be carried in theTraining Announcement Frame.

For FB periods with polling, there may be random access or schedulebased FB. In random access FB, the responder may determine a time slotto transmit the FB using certain random access protocol. xIFS time afterthe polling frame, the responder may transmit the FB frame.Alternatively, the responder may be triggered by the polling frame tostart the random access protocol for the FB transmission. In schedulebased FB, the initiator may poll one responder for the FB. The polledresponder may transmit the FB frame xIFS period after the polling frame.

BF transmission of the FB frame. If antenna/channel reciprocity isassumed, the FB frame may be transmitted using the best sector/beam/AVWtrained in the Training period at the responder side. In this case, thebest transmit sector/beam/AVW may be the same as the best receivesector/beam/AVW trained at the responder side. Otherwise the respondermay utilize a selected sector/beam/AVW or Quasi-Omni weight.

Coding and modulation of the FB frame. The FB frame may be coded andmodulated using the lowest MCS level. Alternatively, the initiator mayassign MCS level for FB in Training frame or Beacon frame. In a thirdmethod, depending on the beamforming scheme used for FB frame, theresponder may determine the MCS used. For example, if the FB frame istransmitted using a trained narrow beam, the responder may utilizehigher MCS level (MCS with higher data rate). if the FB frame istransmitted using a wide beam or Quasi-Omni beam, the responder mayutilize lower MCS level. In one embodiment, the FB period may be used tocarry acknowledgement from the initiator. xIFS time after the end of aFB frame, the responder may expect to receive an acknowledgement framefrom the initiator. The responder may use the trained best receivesector/beam/AVW for the reception. If the responder may not receiveanything after yIFS time period, the responder may consider the failureof FB transmission. yIFS may be longer than xIFS. In cases where each FBtime slot may have a fixed duration, the responder may truncate thetransmission at the boundary. The extra FB frame may be needed tocomplete the feedback procedure.

The responder(s) may expect to receive an acknowledgement frame from theinitiator xIFS period after the end of FB period. Alternatively, theallocation of the acknowledgement period may be signaled in the TrainingAnnouncement Frame. In one embodiment, the responder may receive anM-STA ACK frame which may be a broadcast/multicast frame transmittedfrom the initiator. Each responder may check the per user field in theframe, which may contain a STA ID. If one STA ID may match theresponder's ID, the responder may check the ACK/BA field correspondingto the STA ID. In another embodiment, the responder may receive one ormultiple ACK/BA frames from the initiator. One of the ACK/BA frame maybe addressed to the responder. The responder may check the ACK/BAinformation contained in that frame. Alternatively, the responder mayreceive an ACK announcement frame xIFS time after the end of FB frame.The ACK announcement frame may contain ACK/BA scheduling information tomultiple responders. The responder may determine the time/frequencyoffset of the expected ACK/BA frame corresponding to the announcementframe. The responder to check its ACK/BA frame based on thetime/frequency offset. In the case that the responder does not receiveany ACK or receives a negative ACK in the acknowledgement period, theresponder may determine the failure of the FB transmission. Theresponder may wait for another opportunity to again perform trainingand/or feedback.

Frame Designs

Herein, frames utilized for unified multicast training procedures inexemplary embodiments are described.

Training Frame. A Training Frame may carry training sequences to trainboth initiator transmit beams and/or responder receive beams. Thetraining sequences for initiator transmit beams and responder receivebeams may be designed separately. A Training Frame may or may not carryMAC body. A Training Frames may be broadcast/multicast frames tomultiple users.

A Training Frame PPDU may be designed as shown in FIG. 8, depicting anexemplary frame PPDU design. Depending on the requirement of backwardcompatibility, the Training Frame PPDU may be a DMG PPDU (which isdefined in 802.11ad), a EDMG PPDU (which is defined for 802.11ay), orother type of PPDU. The PLCP header may follow the specified headerformat. The MAC body may be a SSW frame, a BRP frame, a Beacon frame ora newly designed frame. AGC field and TRN-RN field (which is used forresponder receive beam training) may be followed. The sizes of AGC andTRN-RN field may be determined by the number N, which may be signaled inthe PLCP header. 4N is the maximum number of receive beams to be trainedat the responder side.

An exemplary usage of initiator beam pattern and responder beam patternis shown in FIG. 9 for an example beam-training scheme. In this example,it is assumed that N=1, however, it would be easy to extend to any N>1case (and clear to any person of ordinary skill in the relevant art).The initiator may transmit the entire Training PPDU using the sametransmit beam. The responder, however, may use its selected beam forreception of the PLCP header and MAC body. The selected beam may beimplementation dependent. For example, it may be the best known receivebeam corresponding to the initiator, or it may be a Quasi-Omni beam.Starting from the AGC field, the responder may sweep its receive beamsor change its antenna vector weights for receive beam training. In theexample of FIG. 9, there are four AGC subfields, thus, the responder maysweep four beams/weights (say beams 1-4). In the TRN-RX field, there isone channel estimation (CE) sub-field, and four training sub-fields. Theresponder may use the selected beam to receive the CE sub-field and usebeams 1-4 to detect the four training sub-fields. In FIG. 9, thebracketed letters [A], [B], [C], and [D] may represent repeating colorsor any other way to show a repeating pattern.

The MAC body, which may be referred as Training MAC frame may containany or all of the following fields: Transmit address (TA); Receiveaddress (RA); Duration; PAA/Antenna ID; Polarization ID;Beam/sector/codebook ID; CDOWN; and Feedback period requirement. Thetransmit address (TA) comprises transmit MAC address. The receiveaddress (RA) comprises the receive MAC address. In cases where theTraining MAC frame is a broadcast/multicast frame, the RA may be abroadcast/multicast address. Duration comprises the duration to the endof the Training TXOP. The PAA/Antenna ID field may be used to indicatethe PAA/Antenna utilized for this transmission. If a dual polarizationantenna is utilized, the polarization ID may be used to indicate apolarization direction for the transmission. Alternatively, in someembodiments, this field may be omitted and polarization direction may beindicated using PAA/Antenna ID. The beam/sector/codebook ID field may beused to indicate the beam or sector or precoding weight in a predefinedcodebook utilized for this transmission. CDOWN comprises the number ofremaining Training Frames. The Feedback period requirement may carry anyor all of the following subfields: starting time of the FB period;duration of the FB period; FB type; Fixed FB time slot; FB requirement;Acknowledgement included.

The FB type may indicate, for example, the following: polling basedrandom access; polling based scheduled access; random access withoutpolling; scheduled access without polling. Alternatively, this field maybe replaced by two fields. One is poll required field and another is therandom access required field.

Fixed FB time slot may indicate whether the FB time slot is fixed. Inthe case of fixed FB time slot, the time slot duration may be specifiedand/or signaled in the Training Frame.

FB requirement may indicate whether quantized BF is required and/orchannel state information (CSI) is required. The quantized BF may referto PAA ID, Polarization ID, and/or Beam ID feedback. With CSIinformation feedback, CSI of the M strongest taps may be requested forfeedback. M may be signaled in the Training Frame.

Acknowledgement included may indicate whether acknowledgement isincluded in the FB period.

Training Announcement Frame. A Training Announcement Frame may carryinformation for the training period, feedback period, andacknowledgement period. The Training Announcement Frame may bebroadcast/multicast frames to multiple users. The Training AnnouncementFrame may be transmitted using EDMG PPDU, or other types of PPDU. TheTraining Announcement Frame may carry the following fields: TA, RA,Duration, Training Type, training period frequency/time allocation,feedback period frequency/time allocation, acknowledgement periodfrequency/time allocation, number of Training Frames to be transmitted,and number of receive beams to be trained (N is further discussedabove).

TA may be the transmit MAC address. RA may be the receive MAC address.In the case that the Training MAC frame is a broadcast/multicast frame,the RA may be a broadcast/multicast address. Duration may be theduration to the end of the Training TXOP.

Training type may comprise: initiator Tx training; combined initiator Txtraining and responder Rx training; initiator multi-Tx training; orcombined initiator multi-Tx training and responder Rx training. Forcombined initiator Tx training and responder Rx training, a TrainingFrame may contain the TRN-RX field for responder Rx training. Forinitiator multi-Tx training, the initiator may transmit multiple beamssimultaneously for MIMO BF training.

Training period frequency/time allocation may include BW and channelallocation, as well as starting time and duration for the Trainingperiod.

Feedback period frequency/time allocation may indicate if a FB period ispresent. If this field is set, then indicated information may include:BW and channel allocation; starting time and duration for the Feedbackperiod; and/or feedback period requirement. A feedback periodrequirement field may contain the same information disclosed above inrelation to Training MAC frames. In other cases, such as where the fieldis not present, a FB period may be scheduled later.

Acknowledgement period frequency/time allocation may indicate if anacknowledgment period is present. If this field is set, then indicatedinformation may include: BW and channel allocation; and/or starting timeand duration for the Acknowledgement period. In other cases,acknowledgements transmitted from the initiator may be in the FB period.

Alternatively, the Training Announcement Frame may be modified based onGrant frame as defined in 802.11ad.

Opportunistic BF Training. In order to support simultaneous BF trainingfor multiple STAs, an initiator, such as an AP or PCP, may transmit asufficient number of BF training frames in order to provide sufficientinformation of the channel for all STAs with different number of antennaor PAAs and different number of sectors. A STA which is not the intendedtarget of a BF training may be able to receive BF training framesintended for another STA. The STA may provide unsolicited feedback tothe initiator, e.g., an AP or PCP, based on the received BF trainingframes intended for a different STAs, or intended for a group of STAs,which may or may not include the STA itself.

For example, the STA may provide an unsolicited SSW feedback or SSW ACKframe, or a newly designed Unsolicited Feedback frame, to report to theinitiator the best one or more of sector, beam, antenna that it hasreceived. The unsolicited feedback frame may also include informationduring which BF training session such feedback information was obtained;such information may include the IDs (such as MAC address, AIDs, orother types of IDs) of the initiator, responder (which may be a group ofSTAs, identified by a group ID or a broadcast or multicast ID), time ofthe received training sessions, etc. The STA may provide feedback eitherunsolicited or during OFMDA random access, or CBP, or scheduled SP or apre-defined feedback TXOP, or in any other manner.

In another implementation, a STA may establish a long term trainingagreement, and/or unsolicited feedback, and/or a group trainingagreement. STAs and APs and PCPs may exchange the capability of longterm training, and/or unsolicited feedback, and/or group training. Oncesuch agreement is established, the AP or PCPs or any other STAs mayinitiate regular BF trainings according to a schedule or announcementthat is included in beacons or other type of management or controlframes. Once receiving one or more rounds of BF training frames, a STAwith established long term training agreement, and/or unsolicitedfeedback and/or a group training agreement with the initiator mayprovide feedback either unsolicited or during OFMDA random access, orCBP, or scheduled SP or a pre-defined feedback TXOP, or in any othermanner. If a STA has multiple antenna/beam/sectors, and if not allantenna/beam/sectors can be trained using the number of received BFframes, the STA may provide partial feedback. In the partial feedback,the STA may also indicate the number of additional BF frames, sectors,beams that need to be trained. In addition, the STA may also requestadditional training TXOP, e.g., for RSS or responder BF training. TheSTA may provide partial feedback either unsolicited or during OFMDArandom access, or CBP, or scheduled SP or a pre-defined feedback TXOP,or in any other manner.

Random Multi Access of Feedback. The initiator may set up the multipleaccess rule for feedback. In one method, the FB period may be accessedrandomly. In order to reduce the collision probability for randomaccess, a restricted feedback scheme with random access is disclosed.The Feedback period may be partitioned into non-overlapping time slots,on which some access restrictions may be applied. Only the STAs whichsatisfy the restriction may use the time slot to transmit feedbackframe. The restricted feedback period may be announced in a Beaconframe, a Training Announcement frame or specified in the standard. Therestrictions may include one or more of the following:

-   -   The initiator may indicate a group of STAs, which may be within        the coverage range of one or multiple TX sectors/beams of the        initiator to transmit on one or few specified time slots. With        antenna/channel reciprocity assumption, the initiator may assume        the best Rx sector/beam associated with the qualified responders        may be known, and thus the initiator may use the Rx sector/beam        on the corresponding time slot(s) for FB reception.    -   The initiator may indicate a group of STAs, which may perform        certain type of feedback to transmit on one or few specified        time slots. For example, the initiator may indicate: the STAs        which may feedback the best sector ID using time slot group 1;        the STAs which may feedback the best two sectors using time slot        group 2; the STAs which may feedback the CSI using one receive        RX frontend using time slot group 3; the STAs which may feedback        the CSI using two receive RX frontend using time slot group 4;        etc. In this example the time slot may have the same size within        each group, and may be varied from group to group.

FIG. 10 shows an exemplary procedure of sector/beam restricted FB schemewith random access. In this example, in a Training Announcement frame,the initiator may indicate the initiator Tx training using N TrainingFrames to train N beams/sector. The initiator may indicate the FB periodmay contain K time slots, and indicate the restricted random access ruleon each time slot. Alternatively, the restricted random access rule maybe announced by a Beacon frame, or other type of management frame. Or itmay be specified in a standard. In other embodiments, the access may bescheduled or polled.

In the example of FIG. 10, K=N. As such, responders which choose the kthTx beam/sector may reply in the kth random access time slot. In the caseof K>N, more than one random access time slot may be assigned forresponders which may associate with one Tx beam/sector. In the case ofK<N, one random access time slot may be assigned for responders whichmay associate with more than one Tx beams/sectors.

The initiator may transmit the N Training Frames using N sectors/beams.The responders may determine the best Tx beam/sector of the initiator.

In the FB period, the initiator may sweep its receive beams/sectors ondifferent time slots. For a kth time slot, the initiator may use thereceive beam, which may correspond to the kth Tx beam/sector in theprevious Training Period, for reception. As shown in FIG. 10, theinitiator may sweep the receive beams which may have the same/similarantenna setting or beam weight as the Tx beams/antenna weights/sectorswhich were used to transmit the Training frames. The responders whichsatisfy the restriction may contend and transmit. In the example shownin FIG. 10, the responders may be implicitly grouped to N groups. Theresponder group k which considers the kth Tx beam/sector from theinitiator as the best (or one of the best) among all of the Txbeams/sectors may contend for feedback transmission.

In some embodiments, two or more of the procedures described above maybe combined.

In the above mentioned example, the one Training frame may betransmitted each time. In cases where the initiator is capable oftransmitting through multiple beams/sectors simultaneously, two or moreTraining frames may be transmitted through multiple beams/sectors eachtime. In other instances, one Training frame may be transmitted throughmultiple beams/sectors each time. The Training frame may, in oneembodiment, have the format shown in FIG. 8, where TRN-R field may beappended to allow responders to train their best receive beams.

In the above-mentioned example, the FB period may be divided to multipleFB time slots. Each FB time slot may be associated with one sector orbeam direction. Responders which associated with that sector or beamdirection may try to feedback on that time slot, while the initiator mayperform receiving using the associated sector or beam direction. Aresponder may use its best transmit beam, which may be trained using theTRN-R field appended in the Training frame if channel reciprocity isassumed, to feedback on that time slot.

In cases where the initiator has capability to receive through two ormore receive beams simultaneously, each feedback time slot may beassociated to two or more beam directions. For example, the kth FB timeslot may be used for responders which may associate with sector/beamdirections m and n. The initiator, in reception of FB time slot k, mayuse receive sectors/beams m and n correspondingly. The initiator maydesign the sector/beam pair carefully such that the inter-sector/beaminterference at the receiver (initiator) side is small. For example, theinitiator may pair beams/sectors formed through dual polarized PAAstogether.

By using any or all of the above-mentioned procedures, the number ofresponders which may transmit in the same FB time slot may be restrictedand/or limited. However, they may still contend to transmit, since morethan one responder may qualify the transmission restriction. In suchcases, the contention may be performed in the time or the frequencydomain. For example, with time domain contention, each FB time slot mayfurther be divided into an integer number of time chips. Each responderattempting to respond using the FB time slot may randomly select onetime chip to transmit. With frequency domain contention, the widefrequency band may be divided into multiple frequency domainsub-channels. Each responder attempting to respond using the FB timeslot may randomly select one sub-channel on which to transmit. Note thata responder may transmit the preamble or part of the preamble using theentire band, but data fields which may carry the FB information may betransmitted on the selected sub-channel(s). Alternatively, the FB timeslot may be divided into multiple time-frequency domain grids. Theresponder may randomly pick one time-frequency domain unit on or atwhich to transmit. Again, the preamble or part of the preamble may betransmitted over the entire band. The above-mentioned FB procedures maybe extended to transmit data/control information other than beamformingtraining related information.

FIG. 11 depicts an example scenario that includes an AP and multipleSTAs, in accordance with at least one embodiment. The example scenario1100 includes an AP 1102, a STA 1110, a STA 1120, a STA 1130, and a STA1140. In the depicted example, the STA 1110 is a tablet computer, theSTA 1120 is a smartphone, the STA 1130 is a laptop computer, and the STA1140 is a personal digital assistant (PDA). In the depicted example,each of the STAs 1110-1140 receive data from the AP 1102 over a DL asshown at 1111, 1121, 1131, and 1141, and each of the STAs also transmitdata to the AP 1102 over an UL as shown at 1112, 1122, 1132, and 1142.The STAs 1110-1140 may communicate with the AP 1102 (and perhaps withone another) using any suitable wireless protocol, including any IEEE802.11 protocol.

FIG. 12 depicts an example wireless-communication device, in accordancewith at least one embodiment. The device 1200 could be an AP, a STA,and/or any other wireless-communication device. Thus, any of the APs,STAs, and/or other computing-and-communication devices described herein(e.g., the AP 1102, the STAs 1110-1140, etc.) could have a structuresimilar to the example structure that is described in connection withFIG. 12. Moreover, the various devices referred to herein by terms suchas initiator, responder, and the like could have a structure similar tothe structure described in connection with FIG. 12.

As shown in FIG. 12, the example device 1200 includes a communicationinterface 1202, a processor 1204, data storage 1206 containing programinstructions 1208, and an optional user interface 1210, all of which arecommunicatively connected by a system bus 1212. Other devicearchitectures could be used as well, as the provided and describedarchitecture is presented herein by way of example and not limitation.

The communication interface 1202 may include one or morewireless-communication interfaces (for communicating according to, e.g.,LTE, Wi Fi (i.e., any one or more IEEE 802.11 protocols), Bluetooth,and/or the like) and/or one or more wired-communication interfaces (forcommunicating according to, e.g., Ethernet, USB, and/or the like). Assuch, the communication interface 1202 may include any necessaryhardware (e.g., chipsets, antennas, Ethernet cards, etc.), any necessaryfirmware, and any necessary software for conducting one or more forms ofcommunication with one or more other entities as described herein.

The processor 1204 may include one or more processors of any type deemedsuitable by those of skill in the relevant art, some examples includinga general-purpose microprocessor and a dedicated digital signalprocessor (DSP).

The data storage 1206 may take the form of any non-transitorycomputer-readable medium or combination of such media, some examplesincluding flash memory, read-only memory (ROM), and random-access memory(RAM) to name but a few, as any one or more types of non-transitorydata-storage technology deemed suitable by those of skill in therelevant art could be used. The data storage 1206 contains programinstructions 1208 that are executable by the processor 1204 for carryingout various functions described herein.

When present, the optional user interface 1210 may include one or moreinput devices (a.k.a. components and the like) and/or one or more outputdevices (a.k.a. components and the like). With respect to input devices,the optional user interface 1210 may include one or more touchscreens,buttons, switches, knobs, microphones, and the like. With respect tooutput devices, the optional user interface 1210 may include one or moredisplays, speakers, light emitting diodes (LEDs), and the like.Moreover, one or more components (e.g., an interactivetouchscreen-and-display component) of the optional user interface 1210could provide both user-input and user-output functionality. Andcertainly other user-interface components could be used in a givencontext, as known to those of skill in the art.

Although the features and elements of the present invention aredescribed in the preferred embodiments in particular combinations, eachfeature or element can be used alone without the other features andelements of the preferred embodiments or in various combinations with orwithout other features and elements of the present invention.

Although the embodiments described herein consider 802.11 specificprotocols, it is understood that the embodiments described herein arenot restricted to this scenario and are applicable to other wirelesssystems as well.

Throughout the embodiments and provided examples, the blank areas in thefigures implies that there is no restriction for this area and anyembodiment can be employed.

Additional Embodiments. In one embodiment, there is a method comprisingan initiator device transmitting, to a plurality of responder devices, amessage frame containing scheduling information that announces atraining period and a feedback period for MIMO beamforming training; theinitiator device transmitting, to the plurality of responder devices, aplurality of training frames, each frame sequentially transmitted usinga respective transmit beam, during the announced training period, andeach of the training frames having a plurality of training sequencesappended to an end of said training frame, wherein the number oftraining sequences is representative of a number of receive beams of theresponder devices to be trained; the initiator device sequentiallyreceiving beamforming-feedback responses on the receive beams of theinitiator to be trained, said responses received from at least a subsetof the plurality of responder devices during the announced feedbackperiod; and the initiator device transmitting, responsive to thereceived beamforming-feedback responses, one or more acknowledgementframes to the subset of the plurality of responder devices. The methodmay include wherein the initiator device sequentially receives on eachreceive beam to be trained for one of a plurality of time slots withinthe announced feedback period. The method may include wherein within atleast one of the plurality of time slots the initiator device receivesbeamforming-feedback responses from each of a plurality of the responderdevices. The method may include wherein the initiator devicesequentially receives on the receive beams during the feedback period ina same order as used in the training period. The method may furthercomprise the initiator device communicating at least one restrictedrandom access rule indicating requirements for the plurality ofresponder devices to transmit beamforming-feedback responses during eachof the plurality of time slots. The method may further comprise theinitiator device communicating to the plurality of responder devicesinstructions for time domain contention across a within each of theplurality of time slots. The method may include wherein the instructionsdirect responder devices to transmit their beamforming-feedbackresponses in a randomly selected one of a plurality of time chips withina time slot for which said responder device meets the responserequirements. The method may further comprise the initiator devicecommunicating to the plurality of responder devices instructions forfrequency domain contention within each of the plurality of time slots.The method may include wherein the instructions direct responder devicesto transmit their beamforming-feedback responses on a randomly selectedone of a plurality of frequency domain sub-channels within a time slotfor which said responder device meets the response requirements. Themethod may include wherein each training frame includes a PLCP headerthat indicates (i) a basic service set ID that identifies one or both ofthe initiator device and a corresponding basic service set and (ii) anumber of extra training sequences appended to an end of the trainingframe.

In one embodiment, there may be a method comprising an initiator devicetransmitting, to one or more responder devices, a beacon frame thatincludes scheduling information that announces a training period and afeedback period for MIMO beamforming. The method may also comprise theinitiator device transmitting, to the one or more responder devices, anumber N of training frames during the announced training period. Themethod may also comprise the initiator device receivingbeamforming-feedback responses from the responder devices during theannounced feedback period. The method may also comprise the initiatordevice transmitting one or more acknowledgement frames to the one ormore responder devices during an acknowledgement period that occursafter the feedback period. In some instances, the scheduling informationcomprises a starting time and duration of the MIMO beamforming trainingand feedback period. In some instances, the scheduling informationcomprises a time offset relative to the beacon frame. In some instances,each training frame is transmitted using a sector/beam/antenna vectorweight (AVW). In some instances, the training frames are separated by anxIFS period. In some instances, each training frame includes a PLCPheader that indicates (i) a BSSID/Color that identifies one or both ofthe initiator device and a corresponding basic service set (BSS) and(ii) a number K of extra AGC/training sequences appended to an end ofthe training frame. In some instances, each training frame includes aMAC body that contains one or more of a duration, a sector/beam/antennavector weight (AVW) ID, feedback-preference information, andacknowledgement information. In some instances, each training frame iscoded and modulated using a lowest MCS level. In some instances, theinitiator device receiving beamforming-feedback responses from theresponder devices during the announced feedback period comprises theinitiator device receiving multiple feedback frames in multiplerespective time slots. In some instances, the feedback period is afeedback period without polling. In some instances, the respondersutilize random access to transmit the feedback responses. In someinstances, the responders utilize restricted random access to transmitthe feedback responses. In some instances, the initiator repeatssector/beam sweep in the same order as in the training period while theresponder(s) respond in the best sector trained in the training period.In some instances, the responders utilize scheduled access to transmitthe feedback responses. In some instances, the feedback period is afeedback period with polling. In some instances, the responders utilizerandom access to transmit the feedback responses. In some instances, theresponders utilize scheduled access to transmit the feedback responses.In some instances, each feedback time slot begins with a polling frametransmitted from the initiator device. In some instances, each pollingframe is transmitted using a quasi-Omni weight. In some instances, eachpolling frame is transmitted using a lowest MCS. In some instances, eachfeedback time slot other than the first feedback time slot begins with apolling frame transmitted from the initiator device. In some instances,the feedback period is used to carry acknowledgement from the initiatordevice. In some instances, the initiator device transmits amulti-station-acknowledgment frame to multiple responder devices. Insome instances, the multi-station-acknowledgement frame is transmittedusing a quasi-Omni weight. In some instances, themulti-station-acknowledgement frame is transmitted using a lowest MCS.In some instances, the initiator device repeats themulti-station-acknowledgement frame in the time domain. In someinstances, the initiator device repeats themulti-station-acknowledgement frame in the frequency domain. In someinstances, the initiator device repeats themulti-station-acknowledgement frame in both the time domain and thefrequency domain. In some instances, the initiator device transmitsrespective acknowledgement frames to multiple different responders. Insome instances, the respective acknowledgement frames are separated byan xIFS time period. In some instances, each such acknowledgement frameis transmitted using a best sector/beam/antenna vector weight (AVW) thatis selected based on feedback received during the feedback period. Insome instances, the initiator transmits an acknowledgement-announcementframe after an end of the feedback frame. In some instances, aftercomprises an xIFS time after. In some instances, theacknowledgement-announcement frame is transmitted using a quasi-Omniweight. In some instances, the acknowledgement-announcement frame istransmitted using a lowest MCS.

In one embodiment, there is an initiator device comprising: awireless-communication interface; a processor; and data storagecontaining instructions executable by the processor for causing theinitiator device to carry out a set of functions, the set of functionsincluding: transmitting, to one or more responder devices, a beaconframe that includes scheduling information that announces a trainingperiod and a feedback period for MIMO beamforming; transmitting, to theone or more responder devices, a number N of training frames during theannounced training period; receiving beamforming-feedback responses fromthe responder devices during the announced feedback period; andtransmitting one or more acknowledgement frames to the one or moreresponder devices during an acknowledgement period that occurs after thefeedback period.

In one embodiment, there is a unified multicast/broadcastmultiple-in-multiple-out (MIMO) beamforming training procedure, whichincludes: a training period in which an initiator transmits multipleunified training frames for performing a transmit-beamforming trainingof the initiator and a receive-beamforming training of one or moreresponders; a training-feedback period in which each responder replieswith a training-feedback frames; and an acknowledgement period duringwhich the initiator transmits respective acknowledgement frames to theone or more responders. In some instances, each responder transmits atraining-feedback frame using one of a random access, a scheduledaccess, and a poll-based access.

In one embodiment, there is a beamforming training procedure comprising:transmitting from an initiator, multiple unified training frames (UTF)during a training period having a plurality of time slots, wherein atleast one time slot includes simultaneous UTF transmissions overseparate beams. In some instances, the procedure further comprisesreceiving training feedback frames during a training-feedback periodfrom a plurality of responders. In some instances, the FB period isdivided into multiple FB time slots, wherein each FB time slot isassociated with one sector or beam direction. In some instances, the FBperiod is divided into multiple FB time slots, wherein each FB time slotis associated with two or more beam directions. In some instances, thetwo or more beam directions are selected to reduce an inter-sector/beaminterference at an initiator receiver. In some instances, the initiatorforms pairs of beams and/or sectors through dual polarized PAAs. In someinstances, a given FB time slot is restricted/limited, and contention isperformed in either a time or frequency domain. In some instances, atime domain contention comprises dividing each FB time slot into aninteger number of time chips, and wherein each responder contending forthat FB slot randomly selects one time chip during which to transmit. Insome instances, a frequency domain contention comprises dividing thewide frequency band into multiple frequency domain sub-channels, andwherein each responder contending to use a given FB time slot randomlyselects one sub-channel to transmit. In some instances, a respondertransmits a preamble or part of the preamble using the entire band, andtransmits a data field carrying FB information is transmitted on theselected sub-channel. In some instances, the FB time slot is dividedinto multiple time-frequency domain grids. In some instances, aresponder randomly picks one time-frequency domain unit to transmit. Insome instances, the responder transmits a preamble or part of thepreamble over the entire band.

In one embodiment, there is a method comprising an initiator devicetransmitting, to one or more responder devices, a beacon frame thatincludes scheduling information that announces a training period and afeedback period for MIMO beamforming. The method also includes theinitiator device transmitting, to the one or more responder devices, anumber N of training frames during the announced training period. Themethod also includes the initiator device receiving beamforming-feedbackresponses from the one or more responder devices during the announcedfeedback period. The method also includes the initiator devicetransmitting one or more acknowledgement frames to the one or moreresponder devices. The method may include wherein the schedulinginformation comprises a starting time and duration of the MIMObeamforming training and feedback period. The method may include whereinthe scheduling information comprises a time offset relative to thebeacon frame. The method may include wherein each training frame istransmitted using a sector, a beam, or an antenna vector weight (AVW).The method may include wherein the initiator device transmitting thetraining frames further comprises the initiator device concurrentlytransmitting a plurality of training frames using a plurality ofsectors, beams, or antenna vector weights. The method may includewherein the training frames are separated by an xIFS period. The methodmay include wherein each training frame includes a PLCP header thatindicates (i) a basic service set ID that identifies one or both of theinitiator device and a corresponding basic service set and (ii) a numberK of extra training sequences appended to an end of the training frame.The method may include wherein each training frame includes a MAC bodythat contains one or more of: a duration; a sector ID, a beam ID, or anantenna vector weight ID; feedback-preference information; andacknowledgement information. The method may include wherein the number Nis indicated in each training frame. The method may include wherein aremaining number of training frames is indicated in each training frame.The method may include wherein the initiator device receivingbeamforming-feedback responses from the responder devices during theannounced feedback period comprises the initiator device receivingmultiple feedback frames in multiple respective time slots. The methodmay include wherein the length of each time slot is the same. The methodmay include wherein not all of the time slots have the same length. Themethod may include wherein the feedback period is a feedback periodwithout polling. The method may further comprise announcing, from theinitiator device, random access for at least one time slot in which theone or more responder devices may respond. The method may includewherein the random access announcement from the initiator device furthercomprises announcement of restricted random access for at least one ofthe at least one time slot. The method may further comprise wherein thebeamforming-feedback responses from the one or more responder devicesare scheduled by the initiator device. The method may include whereinthe feedback period is a feedback period with polling. The method mayfurther comprise announcing, from the initiator device, random accessfor at least one time slot in which the one or more responder devicesmay respond. The method may include wherein the random accessannouncement from the initiator device further comprises announcement ofrestricted random access for at least one of the at least one time slot.The method may further comprise wherein the beamforming-feedbackresponses from the one or more responder devices are scheduled by theinitiator device. The method may include wherein each feedback time slotbegins with a polling frame transmitted from the initiator device. Themethod may include wherein each polling frame is transmitted using aquasi-Omni weight. The method may include wherein each polling frame istransmitted using a lowest MCS. The method may include wherein eachfeedback time slot other than the first feedback time slot begins with apolling frame transmitted from the initiator device. The method mayinclude wherein the initiator device transmits the one or moreacknowledgment frames to the one or more responder devices during anacknowledgement period that occurs after the feedback period. The methodmay include wherein the one or more acknowledgment frames comprises amulti-station acknowledgment frame to a plurality of the one or moreresponder devices. The method may include wherein the multi-stationacknowledgement frame is transmitted using a quasi-omni weight. Themethod may include wherein the multi-station acknowledgement frame istransmitted using a lowest MCS. The method may include wherein theinitiator device repeats the multi-station acknowledgement frame in thetime domain. The method may include wherein the initiator device repeatsthe multi-station acknowledgement frame in the frequency domain. Themethod may include wherein the initiator device repeats themulti-station acknowledgement frame in both the time domain and thefrequency domain. The method may include wherein the initiator devicetransmits respective acknowledgement frames to multiple differentresponders. The method may include wherein the respectiveacknowledgement frames are separated by an xIFS time period. The methodmay include wherein each such acknowledgement frame is transmitted usinga best sector, a best beam, or a best antenna vector weight (AVW) thatis selected based on beamforming-feedback responses received during thefeedback period. The method may include wherein the initiator devicetransmits an acknowledgement-announcement frame after an end of thefeedback frame. The method may include wherein theacknowledgment-announcement frame is transmitted xIFS time after an endof the feedback frame. The method may include wherein theacknowledgement-announcement frame is transmitted using a quasi-Omniweight. The method may include wherein the acknowledgement-announcementframe is transmitted using a lowest MCS. The method may include whereinthe initiator device transmits the one or more acknowledgment frames tothe one or more responder devices during the feedback period, subsequentto successful decoding of beamforming-feedback responses. The method mayfurther comprise the initiator device transmitting a trainingannouncement frame. The method may include wherein the trainingannouncement frame includes a length of a transmission opportunity. Themethod may include wherein the training announcement frame includes atleast one of a time allocation and a frequency allocation for theannounced training period. The method may include wherein the trainingannouncement frame includes at least one of a time allocation and afrequency allocation for the announced feedback period. The method mayinclude wherein the training announcement frame includes at least one ofa time allocation and a frequency allocation for an acknowledgmentperiod.

In one embodiment, there is a method comprising an initiator devicetransmitting, to one or more responder devices, a training announcementframe that includes scheduling information that announces a trainingperiod and a feedback period for MIMO beamforming. The method alsoincludes the initiator device transmitting, to the one or more responderdevices, a number N of training frames during the announced trainingperiod. The method also includes the initiator device receivingbeamforming-feedback responses from the one or more responder devicesduring the announced feedback period. The method also includes theinitiator device transmitting one or more acknowledgement frames to theone or more responder devices.

In one embodiment, there is a method comprising a responder devicereceiving, from an initiator device, a beacon frame that includesscheduling information that announces a training period and a feedbackperiod for MIMO beamforming. The method also includes the responderdevice receiving, from the initiator device, at least one training frameduring the announced training period. The method also includes theresponder device transmitting a beamforming-feedback response to theinitiator device during the announced feedback period. The method alsoincludes the responder device receiving at least one acknowledgmentframe from the initiator device. The method may further comprise theresponder device determining, based on a received training frame, anumber K of extra training sequences appended to an end of said trainingframe. The method may further comprise, responsive to a determinationthat the number K is greater than or equal to a number of receivingsectors, beams, or antenna vector weights (AVWs) to be trained, theresponder device switching its receiving sectors, beams, or AVWs overall possible combinations. The method may further comprise wherein ifthe number K is greater than the number of receiving sectors, beams, orAVWs to be trained, the responder device repeating at least one of thereceiving sectors, beams, or AVWs to be trained in the at least oneextra training sequence. The method may further comprise, responsive toa determination that the number K is less than a number of receivingsectors, beams, or antenna vector weights (AVWs) to be trained, theresponder device selecting K receiving sectors, beams, or AVWs fortraining. The method may include wherein the K sectors, beams, or AVWsare selected based at least in part on a training history of theresponder device. The method may further comprise the responder deviceestimating a length of the training period. The method may furthercomprise the responder device preparing the beamforming-feedbackresponse based on a type of the announced feedback period. The methodmay further comprise wherein the announced feedback period is randomaccess feedback without polling, the responder device selecting a timeslot to transmit the beamforming-feedback response using a random accessprotocol. The method may further comprise wherein the announced feedbackperiod is scheduled feedback without polling, the responder devicetransmitting the beamforming-feedback response at the beginning of ascheduled time slot. The method may further comprise wherein theannounced feedback period is random access feedback with polling. Themethod may further comprise wherein the announced feedback period isscheduled feedback with polling, responsive to the responder devicereceiving a polling frame, the responder device transmitting thebeamforming-feedback response xIFS period after the polling frame. Themethod may include wherein the received at least one acknowledgmentframe comprises a multi-station acknowledgment frame.

In one embodiment, there is a method comprising an initiator devicetransmitting, to one or more responder devices, scheduling informationthat announces a training period and a feedback period for MIMObeamforming. The method also includes the initiator device transmitting,to the one or more responder devices, a number N of training framesduring the announced training period. The method also includes theinitiator device receiving beamforming-feedback responses from the oneor more responder devices during the announced feedback period. Themethod also includes the initiator device transmitting one or moreacknowledgement frames to the one or more responder devices. The methodmay include wherein the scheduling information is transmitted in abeacon frame. The method may include wherein the scheduling informationis transmitted in a training announcement frame.

In one embodiment, there is a method, comprising transmitting, from aninitiator device to a plurality of responder devices, a message framecontaining training period scheduling information announcing a trainingperiod and a feedback period for MIMO beamforming. The method alsoincludes transmitting, from the initiator device, at least N trainingframes through N beams during the announced training period. The methodalso includes receiving, at the initiator device, at least one feedbacktransmission from at least one of the plurality of responder devices,each of the at least one feedback transmission identifying a preferredbeam for the responder device associated with the feedback transmission.The method also includes transmitting, from the initiator device, atleast a first acknowledgement frame to the at least one of the pluralityof responder devices. The method may include wherein the firstacknowledgment frame is transmitted during an acknowledgment period,wherein the acknowledgment period occurs after the feedback period. Themethod may include wherein the first acknowledgment frame is transmittedduring the feedback period. The method may include wherein the feedbacktransmissions are coordinated by the initiator device according topolling. The method may include wherein the feedback transmissions arecoordinated by the initiator device according to predeterminedscheduling. The method may include wherein the feedback transmissionsare coordinated by the initiator device according to random access. Themethod may include wherein the feedback transmissions are coordinated bythe initiator device according to contention.

1-20. (canceled)
 21. A method, implemented by a first responder device, as one of a plurality of responder devices, the method comprising: receiving, by the first responder device from an initiator device, one or more frames including scheduling information that announces a feedback period, the one or more frames including at least one training field, each respective training field including a plurality of training subfields positioned at an end of a respective frame of the one or more frames; transmitting, by the first responder device to the initiator device, a beamforming-feedback response during a feedback period time slot in the announced feedback period; receiving, by the first responder device using a transmit beam of the initiator device, at least one acknowledgment frame; and on condition that a changed transmit beam from the initiator device is detected, transmitting by the first responder device to the initiator device, one or more unsolicited frames indicating unsolicited feedback information in accordance with the changed transmit beam, wherein: the announced feedback period is a contention-based feedback period such that the first responder device and at least one other responder device can have contending beamforming-feedback responses during the feedback period time slot within the announced feedback period, and the beamforming-feedback response is transmitted on a transmit beam of the first responder device that is associated with a receive beam of the first responder device.
 22. The method of claim 21, wherein the receiving on a first receive beam and one or more further receive beams includes sequentially switching receive beams during a respective training field.
 23. The method of claim 21, further comprising transmitting on a best transmit beam of the first responder device during the feedback period time slot, the best transmit beam being based on a best receive beam of the first responder device.
 24. The method of claim 21, further comprising selecting, by the first responder device, responsive to a number of training subfields: (1) being equal to a number of receive beams of the first responder device to be trained, the number of receive beams to include as receive beams of the first responder device to be trained; (2) being greater than a number of receive beams of the first responder device to be trained, the number of receive beams and at least one repeated receive beam to include as the receive beams of the first responder device to be trained; or (3) being less than a number of receive beams of the first responder device to be trained, a subset of the number of receive beams to include as a set of receive beams to be trained.
 25. The method of claim 21, further comprising: selecting, by the first responder device, responsive to a number of training subfields being less than a number of receive beams of the first responder device to be trained, a subset of the number of receive beams to include as a set of receive beams to be trained, wherein the one or more unsolicited frames indicates any of: (1) one or more additional sectors that need to be trained; or (2) one or more additional beams that need to be trained.
 26. The method of claim 21, wherein the one or more frames received by the first responder device are addressed to more than one of the plurality of responder devices.
 27. The method of claim 21, further comprising determining, by the first responder device, a receive beam of the initiator device used for the feedback period time slot.
 28. The method of claim 21, wherein the receiving of the one or more frames includes receiving, by the first responder device, on a first receive beam during a first training subfield of the plurality of training subfields and on one or more further receive beams during one or more further training subfields of the plurality of training subfields.
 29. A first responder device of a plurality of responder devices, comprising: a transmit/receive unit configured to: receive one or more frames including scheduling information that announces a feedback period, the one or more frames including at least one training field, each respective training field including a plurality of training subfields positioned at an end of a respective frame of the one or more frames, transmit, to the initiator device, a beamforming-feedback response during a feedback period time slot in the announced feedback period; receive, using a transmit beam of the initiator device, at least one acknowledgment frame; and on condition that a changed transmit beam from the initiator device is detected, transmit, to the initiator device, one or more unsolicited frames indicating unsolicited feedback information in accordance with the changed transmit beam, wherein: the announced feedback period is a contention-based feedback period such that the first responder device and at least one other responder device can have contending beamforming-feedback responses during the feedback period time slot within the announced feedback period, and the beamforming-feedback response is transmitted on a transmit beam of the first responder device that is associated with a receive beam of the first responder device.
 30. The first responder device of claim 29, wherein the transmit/receive unit is configured to sequentially switch receive beams during a respective training field.
 31. The first responder device of claim 29, wherein the transmit/receive unit is configured to transmit on a best transmit beam of the first responder device during the feedback period time slot, the best transmit beam being based on a best receive beam of the first responder device.
 32. The first responder device of claim 29, further comprising a processor, wherein responsive to a number of training subfields being equal to a number of receive beams of the first responder device to be trained, the processor is configured to select the number of receive beams to include as receive beams of the first responder device to be trained.
 33. The first responder device of claim 29, further comprising a processor wherein responsive to the number of training subfields being greater than the number of receive beams of the first responder device to be trained, the processor is configured to select the number of receive beams and at least one repeated receive beam to include as the receive beams of the first responder device to be trained.
 34. The first responder device of claim 29, further comprising a processor, wherein responsive to the number of training subfields being less than the number of receive beams of the first responder device to be trained, the processor is configured to select a subset of the number of receive beams to include as a set of receive beams to be trained.
 35. The first responder device of claim 34, wherein the one or more unsolicited frames indicates any of: (1) one or more additional sectors that need to be trained; or (2) one or more additional beams that need to be trained.
 36. The first responder device of claim 29, wherein the one or more frames received by the first responder device are addressed to more than one of the plurality of responder devices.
 37. The first responder device of claim 29, further comprising a processor, wherein the processor is configured to determine a receive beam of the initiator device used for the feedback period time slot.
 38. The first responder device of claim 29, wherein: a first training subfield of the plurality of training subfields is received on a first receive beam during a first training subfield of the plurality of training subfields; and one or more further training subfields of the plurality of training subfields are received on one or more further receive beams during one or more further training subfields of the plurality of training subfields. 